The present invention relates to a method and a device for mounting the constituent elements of the revolving part of a tower crane, this invention being more particularly intended at the construction and mounting of the masthead of tower cranes.
Heavy-duty cranes used on building and civil engineering work sites are generally xe2x80x9ctop turningxe2x80x9d, that is to say have a stationary mast, the height of which can be adjusted by means of additional mast elements, and a revolving top part which can be oriented about a vertical axis and which comprises a delivery jib and a counterjib which constitutes a support for the counterweights.
More specifically, the revolving part of such a crane usually includes a revolving pivot, surmounted by a masthead also known as the xe2x80x9cjib bearersxe2x80x9d, the jib and the counterjib being situated one on each side of the masthead. The jib is articulated by its rear end to the front face of the jib bearer and is held in a roughly horizontal position by means of one or more lines of jib tie rods each obliquely connecting the top of the jib bearer to a point on the jib. Similarly, the counterjib is articulated by its anterior end to the rear face of the jib bearer and is kept in a roughly horizontal position by means of one or more lines of counterjib tie rods each obliquely connecting the top of the jib bearer to a point on the counterjib.
European Patent Application EP 0 635 450 A1, in the name of the Applicant, describes a method for mounting the delivery jib and the counterjib of such a tower crane. According to this method, the jib elements are aligned and assembled on the ground with their tie rods, then the jib tie rods, and possibly those of the counterjib, are raised and aligned using auxiliary lifting gear such as a mobile crane. Next, using the same equipment, the entire jib or counterjib is lifted up with the tie rods, and the jib or counterjib is offered up to the previously mounted masthead so that the free ends of the lines of tie rods are offered up correctly to the top of the masthead, thus allowing the tie rods to be pinned directly to the top of the masthead.
European Patent Application EP 0 846 650 A1 in the name of the Applicant also discloses a method for mounting the tie rods of the jibs of tower cranes, of the kind at issue here, whereby:
In a first step, the counterjib is joined to the base of the already mounted masthead, the end of the tie rod of the counterjib is joined to a mounting strap attached temporarily to the masthead, the strap is raised using a mounting cable which forms lifting tackle between this strap and the top of the previously mounted masthead until the tie rod is aligned, and the counterjib tie rod is pinned to the top of the masthead.
In a second step, the same is done with the jib tie rod or rods, that is to say the jib is joined to the base of the masthead, on the opposite side to the counterjib, by pinning, the free end of the jib tie rod or tie rods is or are connected to a mounting strap attached temporarily to the masthead, this strap is lifted up using the aforementioned mounting cable which forms more lifting tackle between said strap and the top of the previously mounted masthead until the tie rod or tie rods, joined together, are aligned, and the jib tie rod or tie rods is or are pinned to the top of the masthead.
This method too is implemented by initially aligning and assembling the jib elements on the ground, and by using auxiliary lifting gear to offer up the counterjib, and then the jib, against the previously mounted masthead.
This solution proves to be more attractive than the one in European Patent Application EP 0 635 450, particularly in the case of heavy-duty tower cranes, the jibs of which have many tie rods. However, it still has certain drawbacks.
In particular, the method according to document EP 0 846 650 A1 requires special motorization, with an auxiliary winch and tackle or with a handwinch and tackle, to align and pin the jib and counterjib tie rods, hence resulting in a certain amount of constructional complication in the device for implementing the method.
Setting up the tackle needed for aligning and pinning the jib and counterjib tie rods also takes time. This method also ties up the auxiliary lifting gear for a relatively lengthy period of time, which lifting gear has to be used not only for the main handling operations but also during the intermediate operations which are lifting up the counterjib tie rods and the jib tie rods using the aforementioned tackle. Finally, the method under consideration requires several manual pinning assembly operations to be carried out xe2x80x9cup in the airxe2x80x9d, at a certain risk to those involved who have to move along those parts of the crane which are being temporarily held by the auxiliary lifting gear.
What is more, this kind of method entails producing the revolving part of the crane as three xe2x80x9cpackagesxe2x80x9d, namely the xe2x80x9cjibxe2x80x9d assembly, the xe2x80x9ccounterjibxe2x80x9d assembly and the xe2x80x9cjib bearer with tacklexe2x80x9d assembly. This requires a significant amount of space for storing and transporting the constituent parts of the revolving part, and also means that the auxiliary lifting gear has to raise the three xe2x80x9cpackagesxe2x80x9d in succession.
The present invention sets out to avoid these drawbacks, and its object is therefore to provide a method and a device for mounting the constituent elements of the revolving part of a tower crane, of the kind in question, which simultaneously allow:
a reduction in the volume needed for storing and transporting the constituent parts of the revolving part, looking to nest the elements where possible;
a reduction in the number of components and auxiliary parts specific to the crane mounting operations, particularly by eliminating the tackle and its motorization, which previously were dedicated to these operations;
a simplification and limitation on the number of operations of assembling the constituent elements of the revolving part done xe2x80x9cup in the airxe2x80x9d, and making these operations more safe for those involved by reducing the number of handling and assembly operations performed xe2x80x9cup in the airxe2x80x9d, particularly by reducing the number of main packages;
a reduction in the time for which the auxiliary mounting gear, such as the mobile crane, is used.
To that end, the method according to the invention essentially consists, in the case of a tower crane, the revolving part of which comprises a masthead or jib bearer, a delivery jib which is articulated by its posterior end to the front face of the jib bearer and connected to the top of the jib bearer by one or more tie rods, and a counterjib which is articulated by its anterior end to the rear face of the jib bearer and connected to the top of the jib bearer by one or more tie rods:
in assembling, on the ground, an assembly formed by the counterjib, its tie rod or rods and a rear part of the jib bearer which is made in two separable parts, namely a front part and the rear part, and in also assembling on the ground another assembly formed by the jib, its tie rod or rods and the front part of the jib bearer:
using handling or lifting gear, in lifting up the pre-built assembly formed by the counterjib, its tie rod or rods and the rear part, the jib bearer, and in assembling this assembly, by pinning along a horizontal axis, on the revolving pivot or on a mast or mast-cab element connected to this revolving pivot;
using the handling or lifting gear, in lifting up the pre-built assembly formed by the jib, its tie rod or rods and the front part of the jib bearer, and in assembling this assembly, by pinning along a horizontal axis, on the revolving pivot or the mast-cab;
in using at least one pin to join the respective tops of the front part and the rear part of the jib bearer together.
Thus, the invention is based essentially on initially dividing the jib bearer into two parts, a front part and a rear part respectively, which allows two distinct assemblies to be pre-built on the ground, one of these assemblies comprising the counterjib and the rear part of the jib bearer, and the other comprising the jib and the front part of the jib bearer. These two pre-built assemblies are then lifted up in turn and assembled to the revolving pivot or to the top of the mast-cab by pinning. The two constituent parts of the jib bearer are also joined together by pinning, in their upper portions, so as finally to form a complete, rigid jib bearer of triangular or polygonal appearance (when viewed from the side).
Advantageously, the assembling on the ground of the assembly formed by the jib, its tie rod or rods and the front part of the jib bearer is performed by connecting the base of the front part of the jib bearer to the posterior end of the jib root in an articulated manner and by also connecting the front part of the jib bearer to the jib root by a means which restricts the forward and backward pivoting of the front part of the jib bearer relative to the jib. The angular travel thus allowed, for example of the order of 5xc2x0, makes the final operation of connecting the tops of the front part and the rear part of the jib bearer easier.
In one particular embodiment, the operation of assembling on the ground the assembly formed by the jib, its tie rod or rods and the front part of the jib bearer also comprises, for the or each tie rod of the jib, attaching a rear part of the tie rod to the top of the front part of the jib bearer, attaching a front part of that same tie rod to an intermediate point of the jib, bringing the rear part and the front part of the tie rod closer together using a sling pulled by auxiliary handling or lifting gear, and pinning the front end of the rear part of the tie rod to the rear end of the front part of the tie rod. The tie rods are thus pinned together by operations performed on the ground, and are in an aligned position.
The operation of lifting up the assembly formed by the counterjib, its tie rod or rods and the rear part of the jib bearer can be performed, according to a first embodiment, using slings comprising front slings secured to the base of the rear part of the jib bearer and passing over a deflecting member borne by this rear part, and rear slings secured to the structure of the counterjib so as to keep the structure of the counterjib roughly horizontal while this assembly is being lifted and pinned to the revolving pivot or the mast-cab, the tie rod or rods of the counterjib being aligned and taut.
In another embodiment which is an alternative form of the previous one, the operation of lifting up the assembly formed by the counterjib, its tie rod or rods and the rear part of the jib bearer is performed using slings comprising front slings secured to the base of the rear part of the jib bearer, but which are not deflected in any way, and rear slings secured to the structure of the counterjib, the slings being of an appropriate length to keep the structure of the counterjib in an inclined position with respect to the horizontal while this assembly is being lifted and pinned to the revolving pivot or the mast-cab, the rear part of the counterjib being pivoted backward in such a way that the tie rod or rods remain slack: the counterjib structure is brought back to the horizontal and the tie rod or rods are tensioned after said assembly has been pinned to the revolving pivot or the mast-cab.
Given that the assembly comprising the counterjib and the rear part of the jib bearer is built first of all, then the assembly comprising the jib and the front part of the jib bearer is built, the method also advantageously comprises, after the operation of pinning the first of these assemblies to the revolving pivot or the mast-cab, making a temporary connection, with play, holding the rear part of the jib bearer in an upright position while waiting for the top of the front part of the jib bearer to be pinned to the top of said rear part. This temporary connection with play which is not used when the crane is operating, can be made using retaining link rods and slots connecting the top of the rear part of the jib bearer to the revolving pivot or to the mast-cab.
The operation of lifting the assembly formed by the jib, its tie rod or rods and the front part of the jib bearer is also performed using slings, preferably keeping the jib roughly horizontal until such time as it is pinned to the revolving pivot or the mast-cab, then by pivoting the jib upward slightly about the pin used for this pinning so as to approximately pin, with play, the top of the front part to the top of the rear part of the jib bearer. Next, the jib is pivoted in the opposite direction, bringing the rear part of the jib bearer forward, and definitive pinning is carried out. More specifically, the pivoting of the jib in the opposite direction, which brings the rear part of the jib bearer forward on account of its greater weight, causes the hole for the definitive pinning of the top of said rear part to travel along an arc of a circle, the center of which corresponds to the axis for the pinning of the counterjib and the rear part of the jib bearer to the revolving pivot or the mast-cab. During this same time, the hole for the definitive pinning of the top of the front part of the jib bearer travels along another arc of a circle, the center of which corresponds to the axis of pinning of the jib and of the front part of the jib bearer to the revolving pivot or the mast-cab. Through these movements, the respective holes for the definitive pinning of the tops of the two parts of the jib bearer are sure to find a common axis at the point of intersection of the two arcs of a circle mentioned, regardless of the geometric starting position of these pinning holes, and it is thus always possible to perform definitive pinning. As will be understood, this definitive pinning stiffens the jib bearer as required so that the latter can fulfill its function while the crane is operating.
To implement the mounting method defined previously, another subject of the invention is a device which essentially comprises, in combination:
a front part of a jib bearer, including uprights joined rigidly together and fitted at their lower ends with tangs or yoke, collaborating with yokes or with tangs provided at the posterior end of the jib root and with yokes or tangs provided on the revolving pivot or the mast-cab,
a rear part of a jib bearer, separable from the front part and comprising uprights connected rigidly together and fitted at their lower ends with tangs or with yokes, collaborating with yokes or with tangs provided at the anterior end of the structure of the counterjib and with yokes or tangs provided on the revolving pivot or the mast-cab,
the front part and the rear part of the jib bearer also being provided, at their respective tops, with complementing members such as tang and yoke so that these two parts can be pinned together.
According to one embodiment of this device, the front part of the jib bearer is connected, by a prop made up of two unequal portions articulated together, to the posterior part of the jib root, one of the portions of the prop including a member for bearing against the mast root so as to limit the forward and backward pivoting of the front part of the jib bearer with respect to the jib.
According to another advantageous provision, the complementing tang and yoke, provided at the tops of the front part and rear part of the jib bearer, have corresponding anterior and posterior holes for, respectively, the approximate pinning, with play, and the definitive pinning of the tang and the yoke.
Overall, the method and the device for mounting the masthead of tower cranes, which are the subject of the invention, have the following advantages over the prior art:
It is no longer necessary to provide motorization (with its power supply) and tackle for aligning and pinning the tie rods of the jib and possibly of the counterjib, hence providing simplification and a saving.
By eliminating the use of tackle for aligning and pinning the jib tie rods, the invention also affords a time saving in the premounting and mounting operations.
Most of the premounting operations, particularly relating to the assembly formed by the jib, its tie rod or rods and the front part of the jib bearer, and the assembly formed by the counterjib, its tie rod or rods and the rear part of the jib bearer, are performed at ground level, and therefore in complete safety, using light-duty handling gear.
Just two xe2x80x9cpackagesxe2x80x9d, namely, on the one hand, the assembly formed by the jib, its tie rod or rods and the front part of the jib bearer and, on the other hand, the assembly formed by the counterjib, its tie rod or rods and the rear part of the jib bearer, need to be handled in succession by heavy-duty lifting gear (instead of the three xe2x80x9cpackagesxe2x80x9d in the solutions of the prior art).
The operations of handling these two assemblies, using the heavy-duty lifting gear, are performed directly one after the other, without it being necessary, between these operations, to perform other intermediate operations such as lifting the jib and counterjib tie rods; the time for which the heavy-duty lifting gear is tied up is thus minimized.
All the pinning operations which still have to be performed xe2x80x9cup in the airxe2x80x9d are performed vertically in line with the mast of the crane, and therefore without risk to those involved who, in particular, do not have to move around at height along parts of the crane which are held only by the lifting gear.
Being made of two separable parts, each of roughly planar shape, the jib bearer takes up a minimum amount of space for transportation and storage.
This two-part structure of the jib bearer also makes it easier to manufacture, avoiding any volumic mechanical fastening assembly, each part being a simple planar lattice with two uprights connected by cross-members.
The connection between the posterior end of the jib, the base of the front part of the jib bearer and the top of the mast-cab is at a single point, more particularly along the same axis of pinning, thus allowing simple triangulation and thereby avoiding all internal bending moments (couples).
Likewise, the connection between the anterior end of the counterjib, the base of the rear part of the jib bearer and the top of the mast-cab is at a single point, more particularly along the same axis of pinning, thus allowing simple triangulation and thereby avoiding all internal bending moments (couples).